JP4302885B2 - Laser transmission system and method with diffractive optical beam integration - Google Patents

Abstract

A laser delivery system and method incorporate a diffractive optic beam integrator. The diffractive optic apparatus for modifying the spatial intensity distribution of an excimer laser beam (10) to generate a spatially integrated beam comprises a diffractive optic diffuser (12) and a converging lens (22). The diffractive optic diffuser (12) includes a diffractive grating pattern etched in a transparent medium for transforming the intensity profile of the excimer laser beam into a generally circular, substantially uniform spatial intensity distribution at a spatial integration plane. A variable aperture positioned about the spatial integration plane selectively passes the spatially integrated beam to an imaging lens. The imaging lens forms an image of the passed beam about a surface of a tissue to be ablated. A scanning element under computer control scans the imaged beam about the surface.

Description

[0001]
(Field of Invention)
The present invention relates generally to a light beam system for modifying the spatial intensity distribution of a beam, and more particularly to altering the spatial and / or temporal intensity distribution of an excimer laser beam, thereby reducing tissue ablation. And a light beam system for generating a substantially uniform intensity beam.
[0002]
(Background of the Invention)
Excimer lasers have been used in a variety of applications including tissue ablation such as corneal ablation and other surgical procedures. The cross section of the intensity profile of a typical excimer laser beam is typically not spatially uniform. In general, the beam has a substantially rectangular cross section. The intensity along the long axis of the rectangular beam is substantially constant over the central portion of the beam. The intensity along the minor axis of the beam is substantially Gaussian. Thus, the divergence of the excimer laser beam is different along the two axes. As a result, the beam changes shape when emitted and travels away from the excimer laser.
[0003]
Generating a laser beam of substantially uniform intensity is important in many surgical procedures such as tissue ablation, especially in refractive index correction or corneal ablation for therapeutic purposes. Furthermore, the laser beam should maintain the shape required by the ablation algorithm during the ablation procedure.
[0004]
Various methods have been used to modify the spatial illumination or intensity distribution of the laser beam. In order to produce a more uniform intensity beam across the beam cross-section at the ablation plane, researchers have used laser firing capacity and resonators to increase beam uniformity and reduce beam divergence. Changed optics. The mask aperture selects a substantially uniform portion of the beam by truncating the remaining portion of the beam. The aperture is imaged on a resection surface such as the corneal surface. Alternatively, if the beam divergence is sufficiently weak, the beam selected by the aperture can be projected directly onto the corneal surface.
[0005]
Another way to improve beam intensity uses a complex optical system (eg, a set of mirrors, prisms, or lenses) to resolve the beam into a series of beamlets. The beamlets are superimposed in a manner that produces a uniform intensity through the opening of the mask. The opening is imaged on the corneal surface.
[0006]
Yet another method uses a rotatable mask formed with one or more apertures having a geometric helical shape, thereby changing the spatial intensity distribution of the beam. It is disclosed in US Pat. No. 5,651,784, issued to Klopotek, entitled “ROTATABLE APERTURE APPARATUS AND METHOD FOR SELECTION PHOTOABLATION OF SURFACE”. Temporal beam integrators such as rotating dove prisms or k-mirrors are used to modify the laser beam and improve the average non-uniformity of several laser pulses over a time interval.
[0007]
Glockler, US Pat. No. 5,646,791, entitled “METHOD AND APPARATUS FOR TEMPORAL AND SPATIAL BEAM INTEGRATION”, incorporated herein by reference in its entirety, uses a spatial beam integrator to The spatial uniformity of the intensity profile is improved and a separate rotating temporal beam integrator is used to maintain the uniformity of the laser beam intensity over the laser pulse time interval. The spatial beam integrator includes a plurality of prisms distributed around the hollow center. The exit surface of each prism is precisely angled with respect to the body axis of the spatial beam integrator, thereby reflecting the beam toward the center. The spatial beam integrator can be in a steady state to produce a stationary beam with respect to the spatial beam integrator, or can be rotated to produce a rotating beam. The temporal beam integrator includes a pair of rotating cylindrical lenses spaced along the beam axis by a distance approximately equal to the sum of the focal lengths of both lenses.
[0008]
Feldman, US Pat. No. 5,610,733, entitled “BEAM-HOMOGENIZER”, and Case, US Pat. No. 4,547,037, entitled “HOLOGRAPIC METHOD FOR PRODUCING WAVEFRONT TRANSFORMATION”, US Pat. No. 4,547,037. Diffractive optics are used to change the energy distribution of the laser beam. The diffractive optical element is disposed in the laser beam path on the first plane. By properly configuring the plurality of lattice patterns in the first plane, the desired output energy is generated in the second plane.
[0009]
(Summary of the Invention)
Conventional methods of ablating tissue use a complex and expensive device to improve the uniformity of the laser beam. There is a need for a simple and inexpensive device that can convert a non-uniform intensity beam emitted from a pulsed laser into a substantially uniform intensity laser beam over most of the cross-section of the beam. Furthermore, embodiments of the present invention provide temporal integration of the laser beam by providing a means for moving the beam converter between laser pulses.
[0010]
In accordance with one aspect of the present invention, an excimer laser system for tissue ablation comprises an argon fluoride excimer laser and generates a non-uniform beam of pulsed laser energy along an optical path. The non-uniform beam has a non-uniform spatial intensity distribution. The diffractive optical diffuser is spaced from the laser and includes a transparent etched pattern disposed along the beam path, thereby producing a non-uniform beam with a substantially uniform spatial intensity. Convert to a spatially integrated beam with distribution. A positive lens is placed around the diffractive optical diffuser to focus the spatial integration beam to the desired spatial intensity distribution in the spatial integration plane.
[0011]
The present invention uses a diffraction grating technique to change the spatial intensity distribution of the excimer laser beam. Conventional diffraction gratings include apertures or barriers and include a repeating array of diffractive elements. The diffractive element has the effect of generating periodic alternating changes in both phase, amplitude, or sudden waves such as laser beams. One simple arrangement is a barrier with a series of slits that are uniformly spaced from each other. A more common diffraction grating device is a transparent glass plate, where orderly or random parallel cuts are scratched or drawn on the surface of a flat glass plate. The cuts each act as a scattering light source and combine to form a regular array of parallel line light sources. If the grating is totally transparent for negligible amplitude modulation, regular changes in optical thickness across the grating will result in phase modulation. In this case, the diffraction grating device acts as a transmission phase grating. In the present invention, a diffraction grating pattern etched into a transparent medium converts an excimer laser beam into an output beam having a substantially uniform spatial intensity distribution.
[0012]
Another aspect of the present invention is an apparatus for spatially integrating a non-uniform argon fluoride excimer laser beam projected and pulsed along the beam axis and optically for tissue ablation. Excision can be performed. The apparatus comprises means located in the optical path of the non-uniform excimer beam aligned with the beam axis and diffracts the non-uniform excimer beam to generate a spatially integrated beam. The spatially integrated beam has a substantially uniform intensity distribution across the beam cross-section. The converging lens is located in the optical path of the laser beam exiting from the diverging means located around the diverging means and aligned with respect to the beam axis. The converging lens focuses the spatially integrated beam to the desired size and spatial intensity distribution in the spatial integration plane.
[0013]
Another aspect of the present invention is a method of spatially integrating a non-uniform spatial intensity distribution of a non-uniform argon fluoride excimer laser beam that can be optically ablated to ablate tissue. The method includes diffractively diverging a non-uniform beam to obtain a divergent beam having a substantially uniform spatial intensity distribution. The dispersed beam converges on the spatial integration plane. The focused beam is imaged from the spatial integration plane to a plane around the tissue.
[0014]
A further aspect of the invention is a method of spatially integrating a non-uniform spatial intensity distribution of a non-uniform argon fluoride excimer laser beam that can be optically ablated to ablate tissue. The method includes the step of diffractively diverging a non-uniform beam, thereby obtaining a divergent beam having a substantially uniform spatial intensity distribution. The diverged beam is focused on the spatial integration plane. A variable aperture disposed around the spatial integration plane selectively allows the beam to pass. The passed beam is imaged from the spatial integration plane to a plane around the tissue.
[0015]
A further aspect of the present invention is a method for spatially and temporally integrating a non-uniform spatial intensity distribution of a non-uniform argon fluoride excimer laser beam capable of performing optical ablation to ablate tissue. It is. The method includes the step of diffractively diverging a non-uniform beam, thereby obtaining a divergent beam having a substantially uniform spatial intensity distribution. The diverged beam is focused on the spatial integration plane. A variable aperture disposed around the spatial integration plane selectively allows the beam to pass. The passed beam is imaged from the spatial integration plane to the plane around the tissue. Between laser pulses, the moving process moves the diffractive element and provides a temporal integration of subsequent laser pulses.
[0016]
In accordance with another aspect of the invention, a method of surgical tissue ablation using a non-uniform argon fluoride excimer laser beam diffracts the non-uniform beam, thereby substantially increasing the spatial intensity of the top layer. Obtaining a spatially integrated beam having a distribution with a uniform portion. The spatially integrated beam is focused on a spatially integrated plane located in the optical path of the spatially integrated beam. The size and shape of the uniform part of the spatially integrated beam is adjusted by an aperture located around the spatial integration plane. The adjusted uniform portion of the spatially integrated beam is imaged on a plane around the surgical surface.
[0017]
Yet another aspect of the invention is a method of spatially integrating a non-uniform intensity distribution of a non-uniform argon fluoride excimer laser beam that can be optically ablated to ablate tissue. The method includes the step of diffractively diverging a non-uniform beam, thereby obtaining a divergent beam having a spatial intensity distribution with a substantially round top. The diverged beam is focused on the spatial integration plane. The focused beam is imaged from the spatial integration plane to a plane around the tissue.
[0018]
(Description of Preferred Embodiment)
With reference to FIGS. 1 and 2, a substantially rectangular excimer laser beam 10 is projected along the beam axis 11 toward the diffractive element 12. The intensity along the long axis (x-axis) of the beam 10 is substantially uniform. On the other hand, the intensity along the short axis (y-axis) is substantially Gaussian. The diffractive element 12 has a generally planar body 16 that includes a transparent portion 18 that receives and diffractively transforms the laser beam 10. The diffracted beam 20 exiting the diffractive element 12 travels along the beam axis 11 through a positive or converging lens 22 (which converges the diffracted beam 20). The converged beam 30 travels along the optical axis 11 and forms a pattern at the spatial integration surface 32.
[0019]
(Diffraction optical device)
With reference to FIG. 1, the transparent portion 18 has a generally rectangular shape sized to receive the entire rectangular beam 10. However, for non-rectangular beams, it may be desirable for the transparent portion 18 to be circular, square, or other suitable shape that fits the beam 10. The transparent part 18 of the diffractive element 12 has a diffraction pattern etched into a transparent medium. The transparent medium can be a glass-like silica material. The transparent medium is desirably substantially non-absorbing and non-reflecting with respect to the excimer laser beam 10. For example, the transparent medium can include quartz glass, quartz, magnesium fluoride, calcium fluoride, lithium fluoride, or sapphire.
[0020]
The diffraction pattern on the transparent medium forms a diffraction grating, which spatially integrates the non-uniform excimer laser beam 10 with a spatial intensity distribution (which is substantially uniform across the beam cross-section). The excimer beam 20 is configured to be converted. The cross-sectional shape of the converged beam 30 can be circular or rectangular. For ophthalmic surgery (eg, keratotomy), the spatial intensity distribution advantageously has a top-hat shape with a circular central region, which is substantially uniform and converged. Cover most of the cross-section of the beam 30 (see the spatial intensity distribution shown in the spatial integration plane 32 of FIG. 1). Other spatial intensity distributions are possible using different diffraction gratings.
[0021]
The configuration of the diffraction pattern is highly dependent on the desired focused beam 30 shape and spatial intensity distribution. It also depends on the characteristics of the incident beam 10 (for example its wavelength and spatial intensity distribution). The diffraction pattern may include a plurality of suitably spaced regions (eg, lines, spots, etc.). For excimer lasers having short wavelengths near about 193 nanometers (nm), the spacing of the etched regions in the diffraction pattern is advantageously small and accurate. Known etching techniques (eg, dry etching) can be used to etch the diffraction pattern on the transparent portion 18.
[0022]
As shown in FIGS. 1 and 2, the converging lens 22 converges or condenses the beam 20 diffracted as the converged beam 30 onto the spatial integration surface 32. The cross section of the converged beam 30 at the spatial integration surface 32 is substantially circular and has a spatial intensity distribution with a top hat profile. The central region 36 with a uniform intensity distribution desirably covers at least about 70% of the cross section of the beam 30, and more desirably covers approximately 85%. The size of the cross section of the beam 30 at the spatial integration surface 32 is advantageously sized to correspond to the maximum area removed with a single laser pulse. For example, the dimensions across the cross section of the beam 30 at the spatial integration surface 32 can typically range from 3 to 12 mm. 1 and 2 show a flat convex lens, other types of converging lenses 22 may be selected based on the focal length that minimizes aberrations. An anti-reflective coating can be applied to prevent or minimize reflection of the beam 20 from the converging lens 22.
[0023]
In operation, the laser beam 10 is directed along the beam axis 11 through the transparent portion 18 of the diffractive element 12 (which is aligned with the laser beam 10) to receive the entire laser beam 10. The etched diffraction pattern of the transparent portion 18 serves as a diffraction control angle diffuser for changing the spatial intensity distribution of the laser beam 10. The transparent portion 18 converts the generally rectangular Gaussian beam 10 into a generally circular beam 20 having a substantially uniform intensity distribution. A converging lens 22 is aligned with the beam axis 11 and converges the spatially integrated beam 20 to a desired size. The cross section of the converged beam 30 at the spatial integration surface 32 is substantially circular and is uniform in terms of spatial intensity, which is desirable for surgical procedures (eg, corneal ablation).
[0024]
The diffractive element 12 and the converging lens 22 spatially integrate the rectangular beam 10 to form a beam 30 having a substantially uniform intensity profile at the spatial integration plane. The cross section of the beam 30 may be circular or rectangular, or other shapes. With respect to corneal ablation, the beam 30 desirably has a uniform intensity central region 36 that covers at least about 85% of the cross-sectional area of the beam 30. The uniform intensity central region 36 includes a significant portion of the total energy of the rectangular beam 10. This is because there is no significant energy loss through the diffractive optical device. This gives the device high efficiency.
[0025]
The embodiments were tested experimentally with good results using a 193 nm excimer laser. A binary diffractive optics 12 located approximately 15 mm from the 250 mm focal length converging lens 22 produces a uniform circular beam of approximately 12 mm at the spatial integration surface 32. The binary optics used were designed by Digital Optics Corporation of Charlotte (North Carolina). Other companies in the diffractive optics design industry can produce similar gratings. The size of the beam spatially integrated on the spatial integration plane can be changed by changing the focal length of the lens 22.
[0026]
Alternative embodiments of diffractive element 12 that do not require the use of lens 22 may be used. For example, the diffractive lens can be superimposed on the diffraction grating of the diffractive element 12. Such a diffractive element produces a spatially integrated transformed beam at the spatial integration surface 32. Alternatively, the converging lens 22 can be ground on one surface of the diffractive element 12, as shown in FIG. In the illustrated embodiment, the diffractive element 12 can be rotated between pulses to provide temporal integration of the beam.
[0027]
(Application in ophthalmic laser surgery)
FIG. 3 illustrates the application of the present invention to an ophthalmic laser surgical optical system 100 and the relative orientation of components in the system 100. The specific components and configurations described below are for illustrative purposes only. As noted above, diffractive optics devices can be used with a variety of different excimer laser systems.
[0028]
As seen in FIG. 3, the beam 102 is generated from a suitable laser source 104 (eg, an argon fluoride (ArF) excimer laser beam source for generating a laser beam in the far ultraviolet region having a wavelength of about 193 nm). . This wavelength is typically in the range of about 192.5 to about 194 nm. Laser beam 102 is directed to beam splitter 106. A portion of the beam 102 is reflected onto the energy detector 108. Meanwhile, the remaining portion travels through beam splitter 106 and is reflected by mirror 110 onto a rotating temporal beam integrator 112. Another type of temporal beam integrator can be used. The rotated beam exiting the temporal integrator 112 is directed to a diffractive optics device. In the preferred embodiment, the diffractive element 12 is rotated with the beam 102. In the illustrated embodiment, the diffractive element 12 is rotated at substantially the same speed as the beam 102. The beam passes through the diffractive element 12 and the converging lens 22 and exits as a converged beam 30. The converged beam 30 travels to a spatial integration plane 32 where various apertures 116 are arranged. The spatial integration surface 32 is disposed near the focal point of the positive lens 22. An aperture beam 120 emerges from the various apertures 116. The various apertures 116 are preferably irises of various diameters, which are combined with slits (not shown) of various widths, which slits are adapted to specific ophthalmic surgical procedures (eg, optical corneal refractive surgery ( PRK) and optical cornea treatment surgery (PTK)) are used to match the size and profile of the beam 30.
[0029]
The aperture beam 120 is directed onto the imaging lens 122, which can be a biconvex single lens having a focal length of about 125 mm. The imaged beam 126 exiting the imaging lens 122 is reflected by the mirror / beam splitter 130 onto the surgical surface 132. The apex of the patient's cornea is typically positioned on the surgical surface 132. The imaging lens 122 can be moved laterally to a beam that offsets the imaged beam to scan the imaged beam around the surgical surface 132. The treatment energy detector 136 senses the transmitted portion of the beam energy at the mirror / beam splitter 130. The beam splitter 138 and the microscope objective 140 form part of the observation optics. If desired, a beam splitter can be incorporated into the optical path of the beam 134 exiting the microscope objective. The beam splitter is connected to the video camera as needed to assist in observation or recording of the surgical procedure. Similarly, heads-up displays can also be incorporated into the optical path of the microscope objective 140 to provide additional viewing performance. Other ancillary components of the laser optical system 100 (this is not necessary for an understanding of the present invention, eg, a movable mechanical component driven by an astigmatism motor and an astigmatism angle motor. Are omitted for brevity.
[0030]
The diffractive optical device comprising the diffractive element 12 and the positive lens 22 can be used for a variety of laser systems, including scanning laser ablation systems and wide area laser ablation systems. An example is "VISX STAR Excimer Laser System", which is commercially available from VISX, Incorporated of Santa Clara (California). This system produces an output of 193.0 nm, operates at a frequency of 6.0 Hz, and 160.0 millijoules / cm in a 6.0 mm diameter ablation region. ² Adjusted to transmit a uniform flow rate. Other laser systems include T-PRK ^R Scanning and tracking lasers (manufactured by Autonomous Technologies Corporation), SVS Apex lasers (manufactured by Summit Technologies Inc.), Kercor "117 scanning laser systems (manufactured by Chiron Vision), and the like.
[0031]
In an alternative embodiment, the focused beam 30 may generate a central region having a rounded spatial intensity distribution 37 with a spatial integration surface 32, as shown in FIG. This rounded tip distribution 37 can be created by changing the separation between the converging lens 22, the diffractive element 12, and the spatial integration surface 32. Alternatively, a different diffraction pattern at the diffraction element 12 can be used.
[0032]
Spatial integrating beam 30 may desirably be uniform over approximately 85% of the cross-sectional area of beam 30, exceptionally during the laser pulse time interval of beam 30. For such a spatially integrated beam 30, the temporal beam integrator 112 can be eliminated without adverse effects on the characteristics of the beam 30 and the operation of the laser system 100. In that case, the diffractive optical device comprising the diffractive element 12 and the positive lens 22 serves as a spatial beam integrator and does not require a temporal beam integrator. FIG. 4 illustrates an embodiment of the laser optical system 100 without the rotational temporal beam integrator 112 of FIG.
[0033]
The diffractive optical device is simple and inexpensive and does not require rotation by an instrument such as a motor. The diffractive element 12 and the positive lens 22 can be easily aligned with the beam axis 11. A simple diffractive optical device is easy to use and maintain. However, in an exemplary embodiment, the diffractive optical device can be rotated to provide both spatial and temporal beam integrators. The diffractive optical device can be adapted for different excimer laser systems.
[0034]
The ophthalmic laser surgical optical system 100 may use an ultraviolet laser beam in a corneal ablation procedure to ablate corneal tissue in photolysis, which does not thermally damage adjacent and underlying tissue. Molecules at the irradiated surface can be broken down into smaller volatile fragments without heating the remaining substrate; the mechanism of excision is photochemistry (ie, the direct breakdown of intramolecular bonds). Ablation removes the interstitial layer and changes its profile for various purposes (eg, correction of myopia, hyperopia, and astigmatism). Such systems and methods are disclosed in the following US patents and patent publications, the disclosures of which are hereby incorporated by reference in their entirety for all purposes: US Pat. No. 4,665,665. No. 913 (issued 19 May 1987 in “METHOD FOR OPHTHALMOLOGICAL SURGERY”); US Pat. No. 4,669,466 (“METHOD AND APPARATUS FOR ANALYSIS AND COLLECTION OF ABNORMAL FREARCHY 1987”) Issued on March 2, 1988; issued in US Pat. No. 4,732,148 (“METHOD FOR PERFORMING OPHTHALMIC LASER SURGERY”) U.S. Patent No. 4,770,172 ("METHOD OF LASER-SCULPTURE OF THE OPTICALLY USED PORTION OF THE CORNEA" issued September 13, 1988); U.S. Patent No. 4,773,414 ("METHOD OF" LASER-SCULPTURE OF THE OPTICALLY USED PORTION OF THE CORNEA "issued on September 27, 1988); US Patent Application No. 109,812 (filed" LASER SURGERY METHOD AND APPARATUS "on October 16, 1987); Patent No. 5,163,934 (issued November 17, 1992 in “PHOTOREFACTIVE KERATECTOMY”); US Pat. No. 5,556,3 No. 5 ("METHOD AND SYSTEM FOR LASER TREATMENT OF REFRACTIVE ERROR USING AN OFFSET IMAGE OF A ROTABLE MASK" issued on September 17, 1996; US Patent Application No. 08/368, THOR US AND SPATIAL BEAM INTEGRATION "filed January 4, 1995); US Patent Application No. 08 / 138,552 (" METHOD AND APPARATUS FOR COMBINED CYLINDRICAL AND SPHERICAL EY CORTECTIONS "dated 1993; US patent application Ser. No. 08 / 058,599 ( "METHOD AND SYSTEM FOR LASER TREATMENT OF REFRACTIVE ERRORS USING OFFSET IMAGING" in the May 7, 1993 application).
[0035]
The block diagram of FIG. 5 illustrates an ophthalmic surgical system 200 for incorporating the present invention that includes a personal computer (PC) workstation 202 coupled to a single board computer 204 of the laser surgical system 200 by a first bus connection 208. Illustrate. The sub-components of the PC workstation 202 and the laser surgical unit 200 are known components and may include elements of the VISX TWENTY / TWENTY EXCIMER LASER SYSTEM or VISX STAR excimer laser systems, which are Visx of Santa Clara, Calif. , Available from Incorporated. The laser surgical system 200 comprises a plurality of sensors, generally designated by reference numeral 210, which generate feedback signals from movable mechanisms and optical components in the ophthalmic laser surgical optical system 100 of FIG. 3 or FIG. To do. This movable mechanism and optical components include, for example, elements driven by an iris motor 216, an image rotator 218, and an astigmatism width motor 220, and an astigmatism angle motor 222. Scan motor 1 (212) and scan motor 2 (214) are provided for the scanning procedure, where ablation from individual laser pulses is variably offset from the center of the procedure. Transversing the moving lens 122 to the beam 120 provides such a variable offset. The feedback signal from sensor 210 is provided to a single board computer 204 via a suitable signal conductor, which is preferably an STD bus compatible single board computer using an 8031 type microprocessor. . The single board computer 204 controls the operation of the motor drive generally designed with reference number 226 for operating the elements 216, 218, 220 and 222. In addition, the single board computer 204 controls the operation of the excimer laser 104, which is preferably 160 millijoules / cm at the cornea of the patient's eye 230 via the transmission system optics 100 of FIG. 3 or FIG. cm ² An ArF laser with an output of 193 nanometer wavelength, designed to provide a feedback stabilized flow of. Other ancillary components of the laser surgical system 200 (which are not necessary to understand the present invention) (eg, high resolution microscope, video monitor for microscope, system for holding the patient's eye, and ablation waste aspiration) The vessel / filter, as well as the gas transmission system) are omitted to avoid redundancy. Similarly, keyboards, displays, and conventional PC subsystem components (eg, flexible and hard disk drives, memory boards, etc.) have been omitted from the depiction of PC workstation 202.
[0036]
The laser surgical system 200 can be used for procedures such as optical corneal refractive surgery (PRK) and beam therapy keratotomy (PTK). Using the PC workstation 202, the operator inputs at least one patient treatment parameter (eg, a desired change in patient refraction). The treatment parameters described above correspond to improved corneal shape changes. The PC workstation 202 may then calculate a treatment table 260 that includes the positioning of the laser elements during the laser treatment. The laser element, which is typically changed during the procedure, includes the position of variable aperture 116 and lens 112. In PRK, for example, the laser surgical system 200 is used to excise corneal tissue after removal of the epithelium. For correction of myopia, the annular laser beam 30 is adjusted to an annular spot that is registered in the treatment area of the cornea using an adjustable aperture 116. This annular spot is typically a 0.5-6 mm ring. Correction of myopia reduces the curvature of the corneal radius. This requires the removal of more tissue and less tissue in the center of the cornea towards the peripheral treatment area. The first pulse of beam 120 that has passed through the aperture can be removed by removing tissue from the overall treatment area, but the continuous pulse is reduced in diameter by variable aperture 116, thereby making the pulse continuously smaller. In another embodiment, the continuous pulse can be gradually increased from small to large diameter covering the treatment area. This removes more tissue from the central region and makes the cornea a desired profile with reduced curvature. After the optical corneal refractive surgery procedure, the epithelium quickly regrows from the molded area, creating a new anterior surface of the cornea. Alternatively, the epithelium is not removed, but it is partially cut and moved to the side for surgery and returned to its original position after PRK.
[0037]
In an alternative embodiment shown in FIG. 6, the corneal treatment region 300 includes a plurality of smaller regions that are ablated with individual laser pulses, such as an offset image apertured beam 126. The position and size of the smaller ablation area corresponds to the value calculated in the treatment table 260. The reduction in curvature is achieved by the scanning beam 126 for the cornea. As shown in FIG. 6, the offset position 312 of the lens 122 is changed with respect to the central position 310. This scan produces an offset image aperture beam 126 at the external location 308. Desirably, the beam 126 covers the center 302 of the treatment area 300 during the positioning of the scanning treatment. If desired, the dimensions of the variable aperture 116 can be changed during the scan to change the size of the beam 126. In a preferred embodiment, the diffraction optics 12 is moved to rotate between pulses. In the exemplary embodiment, beam rotator 112 and diffraction optics 12 are rotated between pulses. The continuous pulses of the scanning beam are contoured to the desired reduced curvature according to the treatment table 260.
[0038]
For hyperopia correction, the aperture beam 120 of FIG. 3 or 4 scans the treatment area of the cornea. As shown in FIG. 6, the corneal treatment region 300 includes a plurality of smaller regions that are ablated with individual laser pulses, such as an offset image aperture beam 126. The position and size of the smaller ablation area corresponds to the value calculated in the treatment table 260. More tissue should be removed from multiple treatment areas than from the center. This increases the radius of the corneal profile. The profile increase is achieved by scanning the beam 126 for the cornea. As shown in FIG. 6, the offset position 312 of the lens 122 is changed with respect to the central position 310. This scan produces an offset image aperture beam 126 at the external location 308. Desirably, the beam 126 does not cover the center 302 of the treatment area 300 during some scanning procedures. If desired, the dimensions of the variable aperture 116 can be changed during the scan to change the size of the beam 126. In a preferred embodiment, the diffraction optics 12 is moved to rotate between pulses. In the exemplary embodiment, beam rotator 112 and diffraction optics 12 are rotated between pulses. Successive pulses of the scanning beam contour the cornea to the desired increased curvature according to the treatment table 260.
[0039]
For correction of the corneal astigmatism characteristics, variable width slits (not shown) counter measure the treatment area of the cornea, which is generally rectangular. The first pulse of the image aperture beam 126 excises and removes a generally rectangular region of corneal tissue. The continuous pulse is directed by changing the width of the generally rectangular spot of the image aperture beam 126 positioned symmetrically with respect to the optical center. Astigmatism correction changes are made by volumetric removal of corneal tissue.
[0040]
While the above provides a complete and complete disclosure of the preferred embodiments of the present invention, various modifications, alternative constructions, and equivalents can be used where desired. For example, the beam passing through the variable aperture 116 is offset by the transverse movement of the imaging lens 122 in the preferred embodiment, although other scanning elements such as rotating mirrors and prisms can be used if desired. In addition, lasers of appropriate wavelengths other than laser 104 can be used if desired and effective. A laser beam system operating on the principle of thermal ablation, such as a laser having a wavelength in the infrared part of the electromagnetic spectrum, can also be used to implement the present invention. Therefore, the above description and illustrations should not be taken as a limitation of the present invention which is defined by the appended claims.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a diffractive optical apparatus according to an embodiment of the present invention.
FIG. 2 is a front elevation view schematically illustrating the diffractive optical apparatus of FIG.
FIG. 3 is a perspective view schematically showing an embodiment of a laser beam optical transmission system incorporating the diffractive optical apparatus of FIG. 1;
4 is a perspective view schematically illustrating another embodiment of a laser beam optical transmission system incorporating the diffractive optical device of FIG. 1. FIG.
FIG. 5 is a block diagram of an ophthalmic surgical system for incorporating the present invention.
FIG. 6 is a plan view showing an embodiment of the present invention during scanning.
FIG. 7 is a perspective view showing another embodiment of a beam profile having a round-top spatial intensity distribution generated by a diffractive optical device.
FIG. 8 is a plan view of an embodiment having a lens ground on one surface of a diffractive element.

Claims (17)

An excimer laser (104) for generating a non-uniform beam (102) of pulsed laser energy along a path, the non-uniform beam having a non-uniform spatial intensity distribution and a substantially rectangular cross-section ; Excimer laser (104),
An optical diffuser (12) disposed in the path of the non-uniform beam, wherein the non-uniform beam is spatially having a substantially uniform spatial intensity distribution and a substantially circular cross-section. An optical diffuser (12) that converts the beam into an integrated beam;
For tissue ablation comprising a converging lens (22) and a converging lens (22) arranged to focus the beam from the diffractive optical diffuser (12) onto a spatial integration surface Excimer laser system
The diffractive optical diffuser (12) is spaced apart from the laser (104) and has a diffraction pattern disposed across the path of the beam, where the diffraction pattern is An excimer laser system arranged to convert the substantially rectangular non-uniform beam into a substantially circular spatially integrated beam .   The excimer laser system of claim 1, wherein the laser (104) is an ArF laser having a wavelength of about 193 nm.   The excimer laser system according to claim 1 or 2, wherein the non-uniform beam (102) has a spatial intensity distribution substantially following a Gaussian distribution along one axis. The excimer laser system according to any one of claims 1 to 3, wherein the substantially uniform spatial intensity distribution has a top hat type profile having a uniform central region.   The excimer laser system of claim 4, wherein the uniform central region covers about 70% to 85% of the spatially integrated beam cross section.   The excimer laser system according to any one of claims 1 to 5, wherein the diffuser (12) has a transparent portion (18) having the diffraction pattern.   The excimer laser system of claim 6, wherein the diffraction pattern comprises a plurality of spaced apart etched lines.   The excimer laser system according to claim 6 or 7, wherein the transparent portion (18) is substantially rectangular.   9. The transparent part (18) according to any one of claims 6 to 8, comprising a transparent material comprising quartz, or fused silica, or magnesium fluoride, or calcium fluoride, or lithium fluoride, or sapphire. Excimer laser system as described.   The excimer laser system according to any one of the preceding claims, wherein the converging lens (22) is ground on one surface of the diffractive optical diffuser (12).   The excimer laser system according to any one of the preceding claims, wherein the spatial integration plane is arranged around the focal point of the converging lens (22). An excimer laser system according to any one of the preceding claims for shaping the cornea of an eye,
An aperture (116) spaced from the diffractive optical diffuser (12) around the spatial integration plane for passing through the region of the spatially integrated beam;
And a passing beam and the second plane (132) converging lenses spaced from because of the opening (116) directed to (122), an excimer laser system.   The excimer laser system of claim 12, comprising means (216) for adjusting the size of the opening (116). Wherein displacing the beam image of being passed further comprising a order of the scanning means (212, 214), an excimer laser system according to claim 12 or 13. Further comprising an excimer laser system of claim 14, the control means (204) for the scanning means arranged to so that by displacing the image (212, 214) according to the treatment table (260).   The excimer laser system according to any one of the preceding claims, further comprising means (218) for moving the diffractive optical diffuser (12).   The excimer laser system of claim 16, wherein the means for moving (218) is configured to effect rotation of the diffractive optical diffuser (12).

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